Solvent extraction process



J. S. BONNER SOLVENT EXTRACTION PROCESS Filed July 2l. 1955 IPN ATTO IVE 2,417,355 Patented Aug. 12, 1958 ice 2,847 ,35 SLVN' EXTRACTIN PRCESS John S. Bonner, Baytown, Tex., assigner, by niesrre assignments, to Esso Research and Engineering `Company, Elizabeth, N. l., a corporation of Beiaware Application July 2l, 1955, Serial N o. 523,5@0

5 Claims. (Cl. 19o-14.47)

The present invention is directed to a solvent extraction process. More particularly, it is directed to a low temperature solvent extraction operation. In its more specific aspects, the invention is concerned with improving heat transfer in a low temperature solvent extraction operation.

The present invention may be briefly described as an improvement in the low temperature solvent extraction of a hydrocarbon fraction in whichl the hydrocarbon fraction is separated in the extraction zone into an extract phase and a rainate phase. in this operation, a substantially solvent-free first stream is passed in heat exchange relationship in a heat exchange zone with a second solvent-containing stream. In accordance with the present invention, a sufficient amount of a cool component of the-extract phase is introduced into the first U stream at least prior to complete passage through said heat exchange zone in a sufficient amount to form a single liquid phase of reduced viscosity wherein the heat transfer in said heat exchange zone between the streams is improved. Thereafter, the rst stream is returned to the extraction zone.

The first stream may be a hydrocarbon fraction separated from the extract phase and the second stream may be a raffinate phase. The component of the extract phase may be the solvent or the extracted hydrocarbon and the solvent. l

This invention is applicable to any low temperature solvent extraction process in which a solvent is employed at low temperatures to separate one type of hydrocarbons from another type of hydrocarbons. By way of example and not by way of limitation, low temperature sulfur dioxide extraction wherein aromatic hydrocarbons boiling in the gasoline and kerosene boiling range, for

example from about 100 to about 600 F. are separated from aliphatic hydrocarbons and low temperature solvent extractionA of lubricating oil fractions wherein wax is removed employing a solvent, such as a mixture of a ketone and an aromatic hydrocarbon, are exemplary of operations encompassed by the present invention. Other low temperature processes may be employed and other hydrocarbons may suitably be separated in accordance with the present invention.

The ketones employed in. the present invention may be methylethyl ketone, diethyl ketone, ethylpropyl ketone, mixtures thereof, and the like. The aromatic hydrocarbons admixed with the ketones may be benzene, toluene, xylenes, higher 'members of the same hornologous series, mixtures thereof, and the like.

When employing sulfur dioxide as a solvent, the temperatures may suitably range from about 0 to 50 F. and the solvent to hydrocarbon ratio may range from about 1 to 5 expressed as volumes.

When a mixture of a ketone and an aromatic hydrocarbon is employed as a solvent, andy lubricating oil fractions are being extracted, temperatures may range from about 100 to 25 F. with solvent to lubricatin g oil ratios from about 2te 5 expressed as volumes.

from a source not shown.

The amount of the component of the extract phase employed when sulfur dioxide is the solvent may be in the range from about 5% to about 15% by volume of the wash oil. Below about 3% of the component very little beneficial elect is obtained whereas above about 20% there is a decreased capacity and decreased temperature difference in the extraction Zone which olfsets the benefits gained dueA to the present invention.

When other solvents,- such as mixtures of ketones and aromatic hydrocarbons are employed, the amount of the component added will be in the range from about 5 to about 15% by volume. Y

The present invention will be further illustrated by reference to the drawing in which the single figure is a ow diagram of a preferred mode. Referring now to the drawing, numeral 11 designates a feed line in which an aromatic hydrocarbon feed boiling in the range from about 200 to 300 F. is introduced into an extraction tower 12 which is equipped with suitable internal liquidliquid contacting or distributing means whereby intimate contact between liquids is obtained. The aromatic hydrocarbon feed in tower 11 is contacted countercurrently with liquefied sulfur dioxide at a temperature of about 20 F. introduced into tower 12 by line 13 By virtue of the temperature conditions existing in extraction tower or zone 12 a rafnate phase and an extract phase are formed. The raiiinate phase is withdrawn from extraction zone 12 by line 14 and routed thereby into a heat exchange zone 15 designated generally by the dotted lines and comprised of individual heat exchangers 16, 17, andl 18 which will be described in detail more completely hereinafter. The extract phase is withdrawn from zone 12 by line 19 and introduced thereby into a washing tower or zone 20 which is similar to zone 12 and is equipped with suitable internal battling equipment or contacting or distributing means to insure intimate contact between liquids.

In washing zone 20, the extract phase is countercurrently contacte-d with a wash oil introduced by line 21 which has a higher boiling point than the non-aromatic components or the aliphatic hydrocarbons present in the extract phase. The source of this wash oil will be described and discussed more fully hereinafter.` By virtue ofthe washing operation in zone 20, the lower boiling aliphatic hydrocarbons in the extract phase are displaced by the higher boiling aliphatic hydrocarbons in the wash oil `and it is possible, therefore, to make a sharp separation between the aromatics and the higher boiling aliphatics appearing in the washed extract. In any event, a stream which may, be termed a second raffinate phase is withdrawn from washing zone 20 by line 22 and introduced thereby into a sulfur dioxide evaporator or stripper 23 provided with line 24 for withdrawal of sulfur doxide for re-use in the process and with line 25 for introducing the sulfur dioxide-free second raffinate into a fractional distillation tower or splitter 26. The fractional distillation tower 26 is provided with suitable internal vapor-liquid contacting means, such as bell cap trays and the like, to allow separation between the wash oil components in the second raffinate phase and any -aromatic hydrocarbons which may be present therein. The lighter fraction containing aromaticv hydrocarbon is withdrawn from zone 26 by line 27 and after cooling in a cooler or heat exchanger 23 to a temperature of about 20 F. is introduced-into an extraction zone 29 for countercurrent contact with sulfur dioxide introduced thereto by branch line 30 from line 13. By virtue of the extraction taking place in zone 29, a third raffinate phase is obtained and withdrawn from zone 29 by line 31 and admixed with the raii'nate phase in line 1d and a second extract phase is obtained .from .zone 29 andV withdrawn therefrom by line 32 and admixed with the extract phase in line 19 and introduced thereby into Washing zone 20. Withdrawn from washing zone 20 by line 33 is the Washed extract which contains sulfur dioxide and the higher boiling components from the Wash oil which 4havevdisplaced the lower boiling aliphatic hydrocarbons present in the extract introduced into zone 20 by line 19. The washed extract in line 33 is then pumped by pump 34 to an SO2 evaporator or stripper, not shown, for removal of SO2 and nally to suitable distillation equipment for removal of the wash cil components and for recovery of substantially pure aromatics, these `latter facilities also not being shown.

The washV oil components from the fractionator 26 are withdrawn therefrom by line 35 containingT pump -cooled in cooler 37 to a temperature of about 90 F.

and then 'introduced thereby into heat exchange facilities 15 composed of `heat exchangers 16, 17, 'and 1S.

From heat'exchange facilities 15 the cooled wash oil is discharged therefrom by line 21 into washing zone 20 after passing through a chilling Zone Zia'which may be provided therein. The rafnate phase introduced in heat exchange facilities 15 by line 1d is withdrawn therefrom by line 14a and after adjustment of temperature by passage vthrough heater S2 may be stripped of SO2 in stripper S3 which is similar to stripper 23, SO2 being recovered by line 54 for re-use and the raffinate being recovered by line 55 for use as desired.

Makeup wash oil may be introduced into line 35 by way of line 38 containing valve39 and pump d0. On passage of the wash oil through the heat exchanger i5 wherein the temperature of the wash oil is reduced to a temperature in the range from about to about 20 F. the wash oil by virtue of its boiling range which may be in the range from about 400 to 600 F. increases in i viscosity to the extent that heat transfer eciency is lowered. The Wash oil should have a boiling range different from the hydrocarbon feed; generally the boiling range of the Wash oil is higher than the boiling range of the feed. Furthermore, by virtue'of the presence of moisture in the Wash oil, ice may form Within the heat transfer tubes and ultimately plug same causing the process to become inoperable.

In accordance with the present invention there is introduced into the partially cooled wash oil prior to and/ or during its passage through the heat exchanger a sufficient amount of a component of the extract phase to reduce the viscosity of the wash oil and to form a homogeneous liquid phase. This may be accomplished by introducing sulfur dioxide from line 13 by branch f line 41 controlled by valve 42 through a suitable measuring device such as rotameter d3 into line 35 or vby introducing the washed extract from line 33 into line 41 by branch line 44 controlled by valve 45. Also, either sulfur dioxide or the washed extract containing sulfur dioxide may be introduced as spaced apart points as the Wash oil passes in heat exchange with the rainate phase through heat exchangers 16, 17, and 18. It is, therefore, contemplated that either chilled sulfur dioxide or chilled extract plus sulfur dioxide may be introduced by way of lines 46, 47, and 48 controlled, respectively, by valves 49, 50, and 51.

Because of the high viscosity of the wash oil at the best extraction temperatures using sulfur dioxide at F., the heat transfer coeflcient in the heat exchangers is low being frequently in the range from about 10 to about 20B. t. u. per hour per square foot per degree Fahrenheit. When the Chillers `become fouled due to ice formation, the chilling of the wash oil may become a limitation to sulfur dioxide extraction. Therefore, in accordance with the present invention in which liquid sulfur dioxide either as such or in admixture with the extract is introduced at an intermediate point in the chilling circuit at a temperature such that vaporization of sulfur dioxide does not occur and a single liquid phase d exists, the viscosity of the wash oil in the Chillers or heat exchangers is substantially reduced with a substantial improvement in heat transfer coecients.

The amount of sulfur dioxide and/or extract introduced into the wash oil has no significant effect on the operations of the washing tower. As exemplary of the decrease in temperature injection of sulfur dioxide and/ or extract into the wash oil at an intermediate point in the chilling circuit, a temperature difference from about 5 to about 10 F. is obtained. This temperature difference ordinarily may be from about 7 to 8 F. lower than that ordinarily obtainable.

Operations in a commercial unit have increased the capacity and operating time of the unit and have resulted in substantially increased monetary returns and improved operations.

A further advantage of the present invention is that the presence of small amounts of sulfur dioxide in the Wash oil inhibits the formation of ice and sludge on the heat exchange surfaces.

in the present invention it is contemplated that the extraction zone 12, the extraction zone 29 and the washing tower or zone 20 will comprise an extraction'zone since actually the washing or contacting operation is an extraction operation whereby high boiling components in the wash oil replace low boiling components in the extract in the presence of the solvent. In operations where other solvents besides sulfur dioxide are employed, such as in the solvent dewaxing of lubricating oils with a mixture of aromatic hydrocarbons and a ketone and a solvent-free lubricating oil fraction is passed through a heat exchanger the chilling of the solvent-free fraction may make it sui'liciently viscous that heat transfer is substantially impairel. in accordance with this invention, therefore, a component of the extract phase and preferably the ketonearomaticrsolvent would be introduced into the solvent-free lubricating oil fraction at least prior to and/ or during its passage through the heat exchange zone to improve the heat transfer characteristics.

The nature and objects of the present invention having been completely described and illustrated, what l wish to claim as new and useful and to secure by Letters Patent is:

1. ln a low temperature sulfur dioxide extraction of a hydrocarbon fraction boiling in the range from about to about 600 F. in which aromatic hydrocarbons are separated from aliphatic hydrocarbons into a solvent-- containing extract phase and a rainate phase and the extract phase is contacted in a washing zone with an aliphatic hydrocarbon wash oil containing moisture and having a higher boiling range than the aliphatic hydro carbons in the hydrocarbon fraction and in which the rafnate phase containing sulfur dioxide is passed in heat exchange relationship in a heat exchange zone with the wash oil at a sufficiently low temperature such that the viscosity of the wash oil increases to an extent to impair heat transfer eiciency and ice tends to form in said heat exchange zone, the improvement which comprises introducing into the wash oil prior to complete passage through said heat exchange zone a suicient amount of a cooled solvent-containing component of said extract phase to form a single liquid phase of reduced viscosity and to inhibit formation of ice whereby the heat transfer in said heat exchange zone between the raflinate phase and the wash oil is improved, and then returning said wash oil including said solvent-containing component to said washing zone.

2. A method in accordance with claim 1 in which the component is sulfur dioxide.

3. A method in accordance with claim 1 in which the component is the extracted hydrocarbon and sulfur dioxide.

4. A method in accordance with claim l in which the amount of the component is in the range between about 5% and about 15% by volume of the wash oil.

5. A method in accordance with claim 1 in which the cooled component. is introduced into the wash oil at a plurality of points.

References Cited in the le of this patent UNITED STATES PATENTS Grote Jan. 30, 1934 Anson Mar. 2, 1937 6 Van Dijck May 25, 1937 Egli Apr. 19, 1938 Ragatz Mar. 10, 1942 Larson 2 Dec. 28, 1943 Dickinson Nov. 4, 1952 Shelton et al. Y Sept. 21, 1954 Penske et al. Nov. 15, 1955 vI-Iibshman Nov. 22, 1955 

1. IN A LOW TEMPERATURE SULFUR DIIXIDE EXTRACTION OF A HYDROCARBON FRACTION BOILING IN THE RANGE FROM ABOUT 100* TO ABOUT 600*F. IN WHICH AROMATIC HYDROCARBONS ARE SEPARATED FROM ALIPHATIC HYDROCARBONS INTO A SOLVENTCONTAINING EXTRACT PHASE IN AND A REFFINATE PHASE AND THE EXTRACT PHASE IS CONTACTED IN A WASHING ZONE WITH AN ALIPHATIC HYDROCARBON WASH OIL CONTAINING MOISTURE AND HAVING A HIGHER BOILING RANGE THAT THE ALIPHATIC HYDROCARBONS IN THE HYROCARBON FRACTION AND IN WHICH THE RAFFINATE PHASE CONTAINING SULFUR DIOXIDE IS PASSED IN HEAT EXCHANGE RELATIONSHIP IN A HEAT EXCHANGE ZONE WITH THE WASH OIL AT A SIFFICENTLY LOW TEMPERATURE SUCH THAT THE VISOCITY OF THE WASH OIL INCREASES TO AN EXTENT TO IMPAIR HEAT TRANSFER EFFICIENTLY AND ICE TENDS TO FORM IN SAID HEAT EXCHANGE ZONE, THE IMPROVEMENT WHICH COMPRISES INTRODUCING INTO THE ASH OIL PRIOR TO COMPLETE PASSAGE THROUGH SAID HEAT EXCHANGE ZONE A SUFFICIENT AMOUNT OF A COOLED SOLVENT-CONTAINING COMPONENT OF SAID EXTRACT PHASE TO FORM A SINGLE LIQUID PHASE OF REDUCED VISCOSITY AND TO INHIBIT FROMATION OF ICE WHEREBY THE HEAT TRANSFER IN SAID HEAT EXCHANGE ZONE BETWEEN THE RAFFINATE PHASE AND THE WASH OIL IS IMPROVED, AND THEN RETURNING SAID WASH OIL INCLUDING SAID SOLVENT-CONTAINING COMPONENT TO SAID WASHING ZONE. 